MANILA (Reuters) - Philippine environment minister Regina Lopez said on Thursday her order to shut mines operating in watersheds is non-negotiable, and said President Rodrigo Duterte backed her decision.

"It would take a miracle to convince me to allow mining in watersheds. As far as I know it's against the law. It's against social justice, it's against the constitution. He (Duterte) said I agree there should be no mining in watersheds," Lopez told a media briefing.

Lopez on Feb. 2 ordered 23 of the country's 41 mines to shut for alleged environmental violations. Fifteen of the 23 are within watershed areas.

The mines to be closed account for half of nickel ore output by the world's top supplier of the metal. Another five mines were suspended.